Ban stressed the plight of the world's 50 poorest nations, whose population he referred to as the "bottom billion".

"The rising economic tide has not lifted all boats. The poor in 142 of the world's nations are being pulled into the growing global economy. But those of the other 50, the poorest of the world's poor, are not. The global boom has passed them by," he said.

Luiz Ignacio Lula da Silva, Brazil's president, and John Kufuor, his Ghanaian counterpart, also spoke about food and agriculture as the conference got under way.

Lula emphasised the need to find a sustainable solution to the rise in global food prices.

"The food price hikes should not result in strategies for the poorest and the most needy. We must develop mechanisms to ensure that the most needy do not lack food.

Staple crops

Lula spent Sunday with Kufuor inaugurating the Accra headquarters of the Brazilian Agricultural Research Corporation (EMBRAPA), which studies how to improve the production of staple crops such as cassava, rice, beans and soya beans.

In Pakistan and Thailand, army troops have been deployed to avoid food being seized from fields and warehouses

Prices in these countries for foodstuffs such as rice, wheat, sorghum and maize have doubled

Causes of crisis range from financial speculation on food commodities, desertification, population increases, China and India's economic growth and use of grains to make biofuels

Cost of funding projects enabling governments to tackle food crisis could be up to $1.7bn

However, world cereal production in 2008 is projected to increase by 2.6 per cent to a record 2,164 million tonnes

Source: United Nations Food and Agricultural Organisation (FAO)

He said EMBRAPA represented "the spearhead of our conviction to extend to developing countries, and more specifically to African countries, the benefits that EMBRAPA has brought and will continue to bring to Brazil".

But Ghanaian officials have said that EMBRAPA Accra will be one of very few concrete projects resulting from the sharing of technology between developing nations - the much touted South-South co-operation.

Lula hit out at those who have criticised Brazil for letting agricultural land encroach on the Amazon rainforest and growing sugar cane, which is intended for producing bio-fuels, on land that could have been used for food production.

He urged developed countries to look to other parts of the world which still have expanses of arable land.

"They should look towards those countries that did not have opportunities in the 20th century," he said.

"It is precisely the very poor countries that still have a lot of arable land."

He also renewed his call for rich countries - notably the US and EU member states - to do away with farm subsidies.